FISHES FOR CONTROL OF MOSQUITOES, 11 



Wisconsin differ considerably. The stomachs of adult fishes con- 

 tained chiefly entomostracans (Pearse), caddis-fly larvae (Baker), 

 mollusks and insects (Forbes and Eichardson), filamentous algse 

 (Hankinson, Pearse) or silt and mud (Forbes and Richardson, 

 Pearse). Pearse (1918) has studied the stomachs of a number of 

 young roach and found over 90 per cent Entomostraca, a few insect 

 larvae and pupae, water mites, and considerable quantities of fila- 

 mentous algae and Volvox. He sums up (p. 252) : 



Considering all tilings, it appears that when young the golden shiner feeds 

 chiefly on entomostracans, and mature fish on almost any available organisms. 



The author's observations on food were intentionally nearly con- 

 fined to the young in the striped stage. The stomach contents of a 

 few adults varied greatly, in one case consisting entirely of Lemna 

 along with a heavy growth of diatoms and associated protozoans and 

 rotifers. Culex pipiens larvae were plentiful about the margins of 

 the ornamental pond from which this fish was taken. In another the 

 stomach was distended with a mass of winged flies, beetles, and bees 

 to which the fish had evidently risen as they dropped into the water, 

 besides a small quantity of plant remains. This fish was caught on 

 a line in Ridley Creek at a point immediately adjacent to which was 

 a spring- fed swale accessible from the creek through a drainage ditch 

 in which both Culex and Anopheles were breeding freely. In other 

 cases the contents of the stomachs of adults were similar to those of 

 the young, except that the percentage of insects was usually higher. 



The contents of 66 stomachs and intestines of young roach from 28 

 to 65 mm. long are reported in Table 1, page 12. About as many more 

 were examined less thoroughly and found to have similar contents. 

 These consisted chiefly of a dark greenish or greenish slate-colored 

 mudlike mass, largely composed of filamentous algae of various 

 kinds, diatoms, desmids, Protococci, fungus spores, pollen grains, 

 seeds, debris of vascular plants, the tests of protozoans, rotifers and 

 insect eggs, together with some mineral particles. Taking the aver- 

 age of all the stomach contents, this comprised certainly more than 

 one-half, or about 60 per cent of the volume. Next most frequent 

 and abundant were entomostracans of various kinds, sometimes 

 mixed, sometimes almost purely of a particular kind that happened 

 to be abundant. Sometimes the food consisted almost exclusively of 

 Cyclops, Daphnia, or Bosmina. The general percentage of entomos- 

 tracans was estimated at 30 to 35. The remaining 5 to 10 per cent 

 consisted of various insects, water mites, and small quantities of 

 plant tissues. The insects were chiefly chironomid lai-vae and adult 

 flies, including in one case two adult male mosquitoes {Aecles syl- 

 vestris) . In no case were mosquito larvae or pupae detected. 



Observations of the feeding habits of these young both in nature 

 when unalarmed and when confined in aquaria make it clear that a 

 major source of their food is the surface film, consisting chiefly of 

 animal and plant plankton, air-borne dust particles, etc., together 

 with the very similar coating of slime abounding in minute organ- 

 isms which covers the surface of plant stems, exposed roots, and 

 other submerged objects and the surface layer of the bottom ooze. 

 This harmonizes with the nature of the stomach contents and with 

 the results published by Pearse. 



